We have modified our transient absorption spectrometer to dramatically increase the speed of data acquisition and to improve the overall quality of the measured spectra. The instrument has also been interfaced to the advanced laboratory workstation (ALW) network in Building 2 to facilitate storage and analysis of data. We have extended our previous analysis, based on singular value decomposition, of time-resolved spectra measured on component I of trout hemoglobin over a wide range of temperatures. We have identified two early relaxations at low temperature which involve geminate ligand rebinding and deoxyheme spectral changes. The rates of these relaxations are temperature-dependent, but the rebinding yields and the amplitudes of the spectral changes are temperature-independent. These spectral changes have been assigned to tertiary structural changes in photolyzed subunits of the protein. A third relaxation with a temperature-dependent rate and involving a deoxyheme spectral change has also been identified, and we have assigned it to the quaternary structural change of the protein from the R to the T structure. The amplitude of this spectral change decreases as the temperature is increased, which we attribute to a decrease with increasing temperature of the physical size (and therefore spectroscopic effect) of the quaternary structure change of this protein. We are also performing a study of the hemoglobin tetramer using the techniques of molecular dynamics and perturbation free energy simulations.